Turning of threads can be effected by means of tools, the cutting inserts of which have multiple teeth. Usually, such thread-cutting inserts have three to eight teeth, which are of different size and arranged one after the other in a series. More precisely, the tooth that first enters a rotary workpiece has a smallest size in respect of the tooth height, while the next teeth in the series become successively greater and greater up to the last tooth, which is the greatest one and has the contour shape that finally gives the desired profile shape of the thread. Therefore, during one and the same tool pass, the generated thread is given a successively increasing depth, something which reduces the number of required tool passes to a minimum.
On the market, two predominant types of tools are found, which both make use of an insert seat in which the cutting insert is fixed by means of a clamp that is pressed against a plate applied on the top side of the cutting insert and usually being chip breaking, in order to, via the same, clamp the cutting insert, more precisely with the bottom side of the cutting insert abutting against the bottom surface of the insert seat and with the back side of the cutting insert in contact with a rear support surface in the insert seat. A typical example of such a turning tool is disclosed in DE 3740814A1.
Since great amounts of heat are generated during the machining of the workpiece, it is necessary to cool the cutting insert. In practice, this takes place by means of a liquid, which is fed to the teeth of the cutting insert and primarily to the chip-removing cutting edges of the same. It is in respect of the way to cool the cutting insert the two main types of existing tools differ. In both cases, it is true that so-called overcooling is applied, which means that the cooling liquid is flushed out on the top side of the cutting insert via grooves or ducts in the bottom side of the chip breaker plate and is distributed out to the cutting edges of the teeth, which are situated in the plane of the top side. However, in one case, the liquid is supplied via a supply duct, which mouths in the area of the rear support surface of the insert seat and on a level with the interface or the contact surface between the bottom side of the chip breaker plate and the top side of the cutting insert. In the other case, the supply duct for the cooling liquid mouths in the bottom surface of the insert seat, more precisely in line with a hole formed in the cutting insert, which hole extends continuously from the bottom side to the top side of the cutting insert. In other words, the cooling liquid is brought up through the hole in the cutting insert to the contact surface between the top side of the cutting insert and the bottom side of the chip breaker plate, and then it is flushed out towards the tooth edges via the grooves in the chip breaker plate.
However, the cooling of the thread-cutting inserts in the existing tools is unsatisfactory. This manifests itself, among other ways, in a mediocre machining precision and/or a reduced service life of the cutting insert. Hence, there is a considerable need for enhancing the cooling effect with the purpose of reducing the temperature in the cutting insert as well as the immediate surroundings thereof (the workpiece, the chips and parts of the tool). In order to achieve this goal, the eyes of one skilled in the art fall naturally on the possibility of cooling the cutting insert not only from above (overcooling), but also from below (undercooling), because in general terms, undercooling has already earlier been applied in the art in question. Thus, by DE 3004166 A1 a tool intended for the chasing of threads is known, which is constructed in such a way that cooling liquid can be supplied to the cutting insert simultaneously along the top side and along the bottom side. However, in this case, the undercooling is realized by the fact that a special shim plate is formed with recesses through which the cooling liquid can pass out toward the front side of the cutting insert via the bottom side thereof.
Yet, the last-mentioned solution is not a passable way as for the tools already existing on the market, which are frequently occurring in different workshops and together represent great values, in that the tools—and at times also the machines for the same—would need to be rebuilt or modified in a thorough and cost-demanding way for allowing such a solution to be applied.
US 2004/0240949 discloses a thread-cutting which includes a plurality of ducts being connected to a common inlet and having the task of feeding a cooling liquid towards the different teeth of the insert. In this case, however, the ducts are formed in the top side of the insert and terminate at a distance from the cutting edges, the object of the ducts being to provide, by way of a high-pressure cooling liquid, so-called hydraulic wedges between the underside of the released chip and the portion of the top side of the insert which is found between the individual cutting edge and the front end of the individual duct. Therefore, the patent document does not at all concern itself with any undercooling of the insert. In other words the thread cutting insert of US 2004/0240949 is impaired by the same disadvantages as to mediocre total cooling as other known cutting inserts which solely rely on cooling the top side of the insert.